1. Field of the Invention
The present invention relates to fluid shock absorbers, fluid springs, and the like. Particularly, the present invention relates to an electroviscous fluid control device for controlling the flow of fluid in shock absorbers and fluid springs for use in a vehicle suspension system.
2. Description of the Prior Art
Shock absorbers using electroviscous fluid are known. For example, British Patent Application No. 2,111,171 discloses such a shock absorber. The shock absorber includes a cylinder and a piston. The piston is located in the cylinder and divides the cylinder into two chamber portions. Electroviscous fluid fills both of the chamber portions. A passage permits flow of the electroviscous fluid between the chamber portions during relative movement of the piston and cylinder. The viscosity of the electroviscous fluid in the passage is varied by varying the magnitude of an electrical field applied to the electroviscous fluid in the passage. As the viscosity of the electroviscous fluid in the passage increases, the flow through the passage decreases, thereby increasing the damping rate of the shock absorber.
U.S. Pat. No. 3,059,915 discloses a fluid damping device which also uses an electroviscous fluid. The viscosity of the electroviscous fluid varies as a function of the magnitude of a magnetic field applied thereto. Flow of the electroviscous fluid through a passage is controlled by applying the magnetic field to the fluid in the passage. The amount of flow of the fluid through the passage controls the damping rate of the device.
These known devices have the disadvantage that the damping (working) fluid is the electroviscous fluid. Electroviscous fluids are relatively expensive. Since a relatively large volume of the fluid is used in each device, the total overall cost of the device is relatively high.